The present invention is directed to strategies and algorithms by which CDMA networks perform call admission control (CAC) in three different situations: 1) when only common-measurements are available; 2) when no measurements are available; and 3) based on outage probability requirements. In particular, it is applicable to Universal Mobile Telephone Systemxe2x80x94Time Division Duplex (UMTSxe2x80x94TDD) systems.
Call admission control (CAC) is a function responsible for deciding whether to accept or reject a request to setup or reconfigure a radio access bearer in the radio access network (RAN). CAC is performed at the Controlling Remote Network Controller (CRNC). Sometimes, although UE dedicated measurements are not available, common measurements such as uplink timeslot ISCP and downlink carrier power are available. Thus, the CRNC must have the ability to perform CAC properly with only common measurements.
Sometimes, no measurements are available. In this case, the CRNC must have the ability to perform CAC properly in absence of measurements.
In a UMTSxe2x80x94TDD system, the required SIR of a user changes with time because of fading and imperfect power control. In such a system, outage probability is a good measure of system quality of service (QoS). CAC should be designed to provide the required outage probability to the system.
The present invention is able to perform CAC under a variety of conditions. When only common measurements are available, CAC will accept or reject a request based on: 1) common measurements of the target cell and neighboring cells; 2) estimated common measurements after admission; and the measure of the loading of the target cell and neighboring cells, (which are also estimated from common measurements). When the CAC assigns codes of the CCTrCH to different time slots, it will try to optimize the load or carrier power of the target cell and neighboring cells; whereby average or weighted average load/carrier power of the target cell and neighboring cells can be used.
When no measurements are available, CAC accepts or rejects a request based on estimated load of the target cell and neighboring cells. The load may be estimated using the following information: 1) required signal to noise ratio (SIR) of the radio link setup/reconfiguration request, (this represents the load of the request); and 2) required SIR of existing call code-composite transport channels (CCTrCHs) in the target cell and neighboring cells, (this represents the current load of the target cell and neighboring cells). When CAC assigns codes of the CCTrCH to different time slots, it will try to optimize the load of the target cell and neighboring cells; whereby average or weighted average load of the target cell and neighboring cells can be used.
Finally, an alternative embodiment of the present invention can accept or reject a request based on the estimated outage probability of the target cell and neighboring cells. The estimated outage probability is based on assumption of the time-variant SIR. One alternative for estimating the outage probability is to use: 1) required signal to noise ratio (SIR) and SIR range of the radio link setup/reconfiguration request, (this represents the range of load of the request); 2) required SIR and SIR range of existing CCTrCHs in the target cell and neighboring cells, (this represents the current range of load of the target cell and neighboring cells); and 3) the outage probability, which is defined as the probability that the instantaneous load in a time slot exceeds a maximum allowed value. When CAC assigns codes of the CCTrCH to different time slots, it will try to minimize the total outage probability of the CCTrCH, ensuring that the outage probability of assigned timeslots in neighboring cells also meets the requirements.